OVERVIEW: What every practitioner needs to know

Are you sure your patient has a spider bite? What are the typical findings for this disease?

In the United States, two medically important families of spiders exist: Theridiidae or widow spiders and Loxoscelidae or brown recluse spiders. There are five species of widow spiders in the United States, of which the Latrodectus mactans is the most common. Likewise, six species of brown recluse spiders are found in the United States, with Loxosceles reclusa the most prevalent.

Latrodectus mactans (black widow spider) (Figure 1): The initial bite may go unnoticed, but most often is described as a sharp pinch with subsequent pain that develops over the next 30 minutes. A target lesion may appear that has pallor at the site of the bite with surrounding erythema. Other local signs and symptoms of latrodectism may include local diaphoresis, lymphangitis, and/or urticaria. Systemic signs and symptoms typically develop over the next 60 minutes and can include hypertension, muscle cramping, abdominal pain, agitation, diaphoresis, nausea, vomiting, fasciculations, seizures, priapism, and, very rarely, death. Pain and generalized muscle cramping tend to be hallmarks of latrodectism. Untreated, symptoms most often resolve within 48 hours.

Loxosceles reclusa(Brown Recluse Spider) (Figure 2): The bite is most often undetected, with pain ensuing over the next several hours. The bite site may develop a blue macule or a characteristic erythematous lesion with surrounding pallor encircled by an area of cyanosis. Over the next week an eschar may develop and slough. Systemic symptoms associated with loxoscelism can include a flu-like illness with fever, headache, and malaise or, less often, hemolysis, rhabdomyolysis, and renal failure.

Figure 1.

Black Widow source: http://phil.cdc.gov/phil/ID # 9854

Figure 2.

What other disease/condition shares some of these symptoms?

Latrodectism can be confused with an acute abdomen secondary to the significant muscle cramping and abdominal rigidity that can occur with a black widow spider bite. However, while patients with an acute abdomen often prefer to lie quite still, patients suffering from latrodectism are often agitated, hypertensive, and unable to find a comfortable position.

Loxoscelism or necrotic arachnidism can be difficult to diagnose on skin findings alone. The differential diagnosis of dermonecrotic lesions is rather extensive. A few considerations include: contact dermatitis, cellulitis with staphylococcal and streptococcal species, Lyme disease, sporotrichosis, ecthyma gangrenosum, anthrax, herpes simplex, herpes zoster, leukocytoclastic vasculitis, and, of course, bites by other spiders.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Confirming the diagnosis

Confirming the diagnosis of a spider bite is dependent on clinical judgment as well as spider identification. This can be difficult in light of undetected bites that may not be symptomatic for minutes to hours. Clinical toxicology reports indicate that to identify a definite spider bite, clinical signs and symptoms must be present, apprehension of the spider at the time of the bite must occur, and the spider should be identified by an arachnologist. This is particularly true for suspect brown recluse bites because other dermonecrotic wounds have been notoriously misidentified as a brown recluse bite, even in areas where the spider is not endemic.

The American black widow female spider is typically shiny black with red on the ventral aspect of the abdomen. The red coloring may be in the shape of an hourglass. The female spider is larger than the male counterpart, with a body size of approximately 10-15 mm and a leg span of 30-40 mm. The female black widow spider is the one capable of medically relevant envenomation for humans.

The brown recluse spider is known for the violin-shaped marking on its cephalothorax, although this is not consistent across the species. The size of the spider is not sex specific, and both female and male spiders are capable of medically relevant envenomation. The body size is 10-15 mm with a leg span of 25 mm. Most spiders have eight eyes; however, the brown recluse only has six eyes, arranged in pairs. The pairs are arranged in a semi-circle with a space between each pair.

If you are able to confirm that the patient has a spider bite, what treatment should be initiated?

Latrodectism

Local wound care including ice and elevation.

Tetanus prophylaxis should be guided by the patient's immunization history and current guidelines.

Opiates for pain relief and benzodiazepines for muscle cramping and rigidity

Dantrolene and calcium have NOT proved efficacious.

An equine derived Latrodectus mactans antivenom is available and should be considered for severe envenomation (severe pain or systemic toxicity) unremitted by supportive measures. Several case reports also demonstrated resolution of priapism with the administration of antivenom. One vial is typically sufficient. Antivenom should be given in an ER or ICU setting only. Published in 1996, Woestman et al. suggested intravenous antivenom treatment for children experiencing symptoms more than 12 hours or for children with all four symptoms of abdominal pain, hypertension, muscular pain, and agitation or irritability. Consultation with a medical expert is encouraged prior to initiation of antivenom therapy. A medical toxicologist is available through the regional Poison Control Center, 1-800-222-1222 FREE.

Loxoscelism

Local wound care including ice and elevation.

Analgesics

Tetanus prophylaxis should be guided by the patient's immunization history and current guidelines.

Prophylactic antibiotics are not indicated; however, if secondary infection occurs then antibiotic usage is recommended.

In cases of significant necrosis, excision and skin grafting may be necessary. However, this is not recommended for at least 6 weeks.

In cases of severe envenomation that leads to hemolytic anemia, treatment with red blood cell transfusions and intravenous fluids may be necessary. Plasma exchange for both correcting coagulopathy and clearing the plasma in order to restore routine lab monitoring affected by severe hemoglobinemia has also been reported.

Antivenom is not available in the United States.

What are the adverse effects associated with each treatment option?

Acute and delayed hypersensitivity reactions can occur with receiving antivenom. However, the reported incidence of anaphylaxis or serum sickness secondary to Latrodectus mactans antivenom is low, especially when appropriately diluted and given as a slow infusion.

What are the possible outcomes of spider bites?

Latrodectism very rarely ends in death. Typically, symptoms last 24-48 hours. Antivenom can decrease pain and shorten the duration of the illness.

Loxoscelism most often is self-limited, and the bite site heals without complication over several days to a week. Presence or absence of local signs and symptoms does not correlate well with the likelihood of developing systemic symptoms. If the bite site becomes necrotic, then an eschar with subsequent ulceration may occur. Such lesions can take months to fully heal, although many resolve over several weeks without surgical intervention or permanent scarring.

What causes this disease and how frequent is it?

Approximately 40,000 species of spiders have been identified worldwide, of which there are 30 Latrodectus species and 100 Loxosceles species. Of these, five species of Latrodectus are found in the United States, (L. mactans, L. hesperus, L. variolus, L. bishopi, and L. geometricus or brown widow). While the brown recluse spider or L. reclusa is the most prevalent in the United States, five other species exist and are predominately found in the Southwest, (L. apachea,L. arizonica, L. blanda, L. deserta, and L. devia). L. reclusa is found in Texas, Oklahoma, Kansas, Arkansas, Louisiana, Nebraska, Missouri, Iowa, Ohio, Illinois, Indiana, Kentucky, Tennessee, Mississippi, Alabama, and western Georgia. During the time frame 2007 through 2009, between 10,000 and nearly 14,000 spider bites/envenomations were recorded by the American Association of Poison Control Centers, with no deaths reported. Of these, approximately 20% of the black widow bites/envenomations, as well as the brown recluse bites/envenomations, were in persons ages 19 and under, yearly.

The widow spiders and brown recluse spiders prefer warmer temperatures, and encounters are likely to occur in warmer months. They gravitate to dark locations and can be found both indoors or outdoors. Most encounters are incidental and occur because the spider has crawled into a dark, dry, and discrete location such as a shoe, glove, infrequently used clothing, or bed linens. They then become pressed up against the patient's skin when one of these items is put on, and then a bite occurs. Further, the spiders may be found in garages, attics, basements, or other rarely disturbed corners of a home. Outside, spiders may be found under rocks, woodpiles, or other such locations. The brown recluse, in particular, is nocturnal and shy and has been reported in large numbers in homes within endemic areas without any reported bites. This re-emphasizes the point that bites in non-endemic areas are unlikely.

How do these pathogens/genes/exposures cause the disease?

Loxosceles venom, like many other venoms, is a complex mixture of enzymes and other biologically active components. The most important enzyme is sphingomyelinase D, which is responsible for endothelial damage, tissue necrosis, platelet aggregation, and hemolysis.

Latrodectus or black widow venom contains a neurotoxin, alpha-latrotoxin. The toxin works through calcium-mediated mechanisms to cause significant release of neurotransmitters presynaptically at neuromuscular junctions. The release of neurotransmitters such as acetylcholine and norepinephrine, among others, causes activation of the sympathetic and parasympathetic nervous systems. The venom also blocks re-uptake of the neurotransmitters.

Are additional laboratory studies available; even some that are not widely available?

Within the literature are studies regarding Loxosceles venom detection by immunoassay, as well as investigation of the best medium for venom recovery.

How can spider bites be prevented?

In an effort to avoid spider bites, consider shaking out gloves, clothes, shoes, and such before putting them on. When engaged in outdoor activities that might bring you in contact with spiders, wear long-sleeved shirts and pants as well as gloves. Appropriate insecticide use within homes and topical use for clothing or skin when outdoors may provide additional protection.